It has been a widely established practice to perform a tomosynthetic process by applying radiation to a target object (for example, a subject) from a plurality of respective different angles, detecting radiation that has passed through the target object with a radiation detector, converting the detected radiation into respective radiographic images (projected images), and processing the converted projected images in order to reconstruct a tomographic image at a desired sectional position in the target object. (See, for example, Japanese Laid-Open Patent Publication No. 2007-130487, Japanese Laid-Open Patent Publication No. 2009-192384, and Japanese Laid-Open Patent Publication No. 2012-512669 (PCT)).
The tomosynthetic process may be combined with a plain image capturing process for applying radiation to a target object from an angle (0°) in front of the target object, detecting radiation that has passed through the target object with a radiation detector, and converting the detected radiation into a radiographic image (plain image). Acquisition of such a plain image is not limited to acquisition by a plain image capturing process, which is carried out separately from the tomosynthetic process. For example, the tomosynthetic process may include, as a portion thereof, a process for producing a projected image, which is acquired by applying radiation to a target object from an angle of 0° as a plain image, or a process for generating a pseudo-plain image based on respective tomographic images at a plurality of sectional positions.
For displaying each of the acquired tomographic images and the plain image on an image display device, it has heretofore been customary to provide the image display device with a single display unit having two display areas on a screen thereof, or two display units having respective display areas on screens thereof, and to successively display the tomographic images in one of the display areas, while at the same time displaying the plain image in the other display area. Successively displaying tomographic images refers to displaying the tomographic images at respective sectional positions successively one after another, to thereby display a pseudo-three-dimensional image (hereinafter also referred to as a “reconstructed image”) of the target object, which is reconstructed from the tomographic images.